Original paper
Lytoceratids (Cephalopoda, Ammonoidea) from the Lower Posidonienschiefer Formation (Tenuicostatum Zone, Early Jurassic) of Baden-Württemberg (south-western Germany)
Maisch, Michael W.; Hoffmann, René
Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen Band 283 Heft 3 (2017), p. 275 - 289
published: Mar 1, 2017
ArtNo. ESP155028303002, Price: 29.00 €
Abstract
The rare finds of lytoceratids from the Lower Posidonienschiefer Formation (Early Toarcian, Tenuicostatum Zone) of south-western Germany are reviewed and new material is described. These forms have previously been assigned to Holcolytoceras nodostrictum (Quenstedt, 1885) and Lytoceras fimbriatum (Sowerby, 1817). Holcolytoceras spath, 1924 is otherwise restricted to the Early Pliensbachian (Ibex Zone) of Germany, Austria and Hungary. The specimens from the Tenuicostatum Zone do not representHolcolytoceras, but are small, indeterminable lytoceratids most probably referable to Lytoceras suess, 1865 or to Alocolytoceras hyatt, 1900.Lytoceras fimbriatum (Sowerby, 1817) is also an otherwise exclusively Pliensbachian taxon. Its record from the Early Toarcian Tenuicostatum Zone is based on a single, ill-preserved specimen. An additional, much better preserved specimen of the same taxon definitely shows that it does not represent L. fimbriatum but a potentially new species of the genus Lytoceras, characterised particularly by its very regular, fine, prorsiradiate ribs and the complete absence of flares and/or constrictions throughout ontogeny. The Toarcian records of Holcolytoceras nodostrictum and a late survival of the Ectocentritinae, as well as the early Toarcian occurrence of L. fimbriatum are not confirmed.
Keywords
pliensbachian • posidonienschiefer formation • holcolytoceras • lytoceras • toarcian • taxonomy • stratigraphy • ammonitida